Flame treating of paperboard and method therefor

ABSTRACT

An apparatus and method for flame treating paperboard. A plurality of burners are mounted to a flame and are positioned to have continuous flames extending therefrom toward the paperboard. Each burner is hollow and is connected to a source of gas/air mixture. The gas is mixed with sufficient air prior to ignition to insure complete combustion. Each flame has an intense and lean characteristic with the flame either impinging or spaced from the paperboard. A plurality of air curtains are positioned to convey away combustion by-products of those flames which have a downward orientation.

[ Mar. 11, 1975 United States Patent 1 1 ise [54] FLAME TREATING OF PAPERBOARD AND 3,562,920 2/1971 Vuilleumier et 156/497 METHOD THEREFOR Primary Examiner.lohn J. Camby [76] lnvemor' gggi g g ga g' gy 27066 Attorney, Agent, or Firm-Woodard, Weikart,

Emhardt & Naughton [22] Filed: Feb. 5, 1974 [57] ABSTRACT An apparatus and method for flame treating paper- App]. No: 440,083

board. A plurality of burners are mounted to a flame and are positioned to have continuous flames extending therefrom toward the paperboard. Each burner is hollow and is connected to a source of gas/air mixture.

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insure complete combustion. Each flame has an in- [561 :1:111232.211???2131;321:32111111231,;

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UNITED STA TES PATENTS air curtains are positioned to convey away combustion 1,434,207 10/1922 by products of [hose flames have a downward 1,677,492 7/1928 432/230 Orientation $021,125 2/1962 Stuchbery........................... 432/230 3,236,160 2/1966 Mullancy 432/231 15 Claims, 4 Drawing Figures PATENTEB MRI 1 I975 ShLEI l UF 2 HJQ PATENTEB NARI 1 I975 SHEEIEQFZ FLAME TREATING OF PAPERBOARD AND METHOD THEREFOR BACKGROUND OF THE INVENTION Field of the Invention This invention is in the field of heat treating devices. Many of the prior art devices utilize a rich mixture of gases which produces a reducing flame, characterized by an inner primary mantle that burns with less than the ideal aeration necessary for complete combustion. When flame treating sheets of paper or other laminates with this type of flame, interception of the flame envelope with the leading edge at the base of the flame or at the end of the primary mantle zone of the flame causes this rich mixture to imbed in the boundary layer surrounding the leading edge. Wrap-around of the heat and flame to the opposite side of the paper surface also occurs frequently causing adhesion to the wrong side. Reignition ofthe gases in the boundary layer can occur, which scorches or burns the material surface. Scorch is highly undesirable, particularly in the construction of food cartons where both good appearance and aseptic quality must be maintained.

Disclosed herein is an apparatus and method for flame treating an item with a flame resulting from a lean mixture of gas and air thereby providing an oxidizing atmosphere. Complete one-step combustion of the fuel is effected, yielding an intense, sharp flame with a high level of ionization. The combustion arrest and boundary layer reignition are greatly precluded with this oxidizing flame. The flame does not engulf the edge of the item being treated as distinguished from the flames produced by the prior art devices. The apparatus and method disclosed herein is described in terms of treating paperboard; however, it is to be understood that other items may be treated by the flame according to the present apparatus and invention. For example, the flame may be utilized to laminate plastic to paper and to aluminum foil.

A major disadvantage of many of the prior art devices is the large amount of mass required in the burners. The large mass type burners absorb a large amount of heat thereby allowing accidental ignition of the paperboard when the flame is extinguished and the conveying means transporting the paperboard slows or stops. The flame burners disclosed herein are designed to have low mass thereby minimizing the heat retained by the apparatus.

Some of the prior art burners have corrugated screen forming the mixture outlets. As a result, the gas/air mixture flows slowly outwardly from the burner in a manner similar to a home stove. The burners disclosed herein have spaced-apart gas outlets which are idealized precision orifices sized with respect to the internal cross-section of the hollow interior of the burner in such a manner that the mixture is forced out with greater velocity thereby increasing the heat transfer while also minimizing the amount of gas which exits the burner. The ideal precision design of the burners disclosed herein is essential to the creation of a stable high-Velocity oxidizing flame. The high-velocity capability promotes aspiration of ambient air to insure complete fuel oxidation. In addition, due to the greater heat transfer rate, the paperboard may be conveyed past the burners at a much greater speed. For example, the paperboard treated in accordance with the present invention may be conveyed at a speed greater than four times the conveying speeds possible with the prior art devices. The greater thermal efficiency developed by the lean flame promotes better fuel gas economy.

Another advantage of the method disclosed herein is the high level of ionization provided in the lean flame. Treatment with this type of flame prior to laminating or joining substrates achieves bond strengths and seal quality far superior to those produced by treatment with the rich, reducing flames of some of the prior art devices.

SUMMARY OF THE INVENTION One embodiment of the present invention is an apparatus for flame treating paperboard comprising a frame, a source of gas under pressure of at least 0.20 psi, valve means mounted on the frame operable to mix air with the gas to produce a blue, lean flame when the gas is ignited, a first elongated tube with a longitudinal axis, the tube being mounted on the frame and connected to the source to receive gas therefrom, the tube having an interior cross-sectional area extending perpendicular to the axis, the tube having a plurality of gas outlets extending along the longitudinal axis with the cross-sectional area of the tube being at least three times the area of the gas outlets forcing the gas and the air out through the outlets at high velocity producing an intense, rapid flame when ignited, a pair of opposite flame directing walls on the tube and extending along the axis with the flame extending between the walls being compressed therebetween, the walls are spaced apart forming a trough in which the gas burns, each of the Walls including heat expansion slots positioned along the axis, and conveying means mounted on the frame and supporting the paperboard operable to convey the paperboard past the trough and the flame therein.

Another embodiment of the present invention is a method of flame treating paperboard while preventing scorching thereof comprising the steps of forcing a gas- /air mixture from outlets extending along the length of an elongated tube under sufficient pressure to produce a first intense, continuous flame extending the length of the tube when ignited, pre-mixing sufficient air with the gas prior to the forcing step to insure complete combustion of the gas, and igniting the mixture.

It is an object of the present invention to provide a new and improved flame treating apparatus.

A further object of the present invention is to provide a new method of flame treating.

Related objects and advantages of the present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective fragmentary view of an apparatus incorporating the present invention.

FIG. 2 is an enlarged cross-sectional view taken along the line 2--2 of FIG. 1 and viewed in the direction of the arrows.

FIG. 3 is an enlarged bottom view of one of the sealer burners shown in FIG. 1 looking upwardly in the direction of arrows 3-3.

FIG. 4 is a schematic representation of the apparatus of FIG. I used to flame seal a paperboard.

DESCRIPTION OF THE PREFERRED EMBODIMENT For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It .will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

Referring now more particularly to FIG. 1, there is shown an apparatus for flame sealing paperboard which has a meltable coating thereon. Apparatus 10 includes a main frame 11 with four sealer burners 12 through mounted thereon. Sealer burners 12 and 13 each direct a straight, continuous flame downwardly against the top surface of the paperboard whereas sealer burners 14 and 15 each direct a straight, continuous flame upwardly against the bottom surface of the paperboard. In addition, a pair of air nozzles 16 and 17 are mounted to frame 11 with each air nozzle directing an air curtain upwardly to convey away combustion byproducts from the flames emitted by flame sealers 12 and 13.

A solenoid valve 18 is connected to a gas line containing gas at an approximate pressure of four to twelve ounces per square inch. Solenoid valve 18 in turn is connected through a gas regulator 19 to a gas manifold 20 including four outlet conduits 21 with each conduit being provided with a gas cock 22 and a flow control valve 23. A separate conduit 24 is connected to each flow control valve 23.

Air filter 29 is connected to air compressor 30 which sucks atmospheric air through the filter and then forces the air through pipe 31 which is in communication with a hollow manifold 25. Four venturi housings 32 through 35 are mounted directly beneath housing with the air within housing 25 flowing outwardly through apertures into venturi housings 32 through 35. Venturi housings 32 through 35 are also in communication with the four gas conduits 24 with four adjustment valves 36 provided on housing 25 to control the flow of air from housing 25 into venturi housings 32 through 35. Meters 37 indicate the air pressure applied from housing 25 to a venturi within each venturi housing. The desired amount of air and gas is mixed within each venturi housing and then routed out through air/gas conduits 26 each having an opposite end connected to flexible metal hoses 28. Hoses 28 are connected to sealer burners 12 through 15. A clean-out plate 38 is mounted to the end of housing 25 to facilitate cleaning of the housing.

Sealer burner 13 will now be described it being understood that a similar description applies to sealer burners 12, 14 and 15. The main body of sealer burner 13 has a hollow interior 40 which is connected to flexible metal pipe 28 to receive the gas/air mixture therefrom. Groups of three outlets 41, 42 and 43 are provided at one edge of the main body along the length of the burner allowing the gas and air to escape therefrom at a controlled rate. Outlets 41, 42 and 43 are precision drilled ports as compared to the random, irregular apertures in the prior art ribbon burners. As a result, the total cross-sectional area of the gas outlets is strictly controlled with respect to the internal cross-sectional area of each burner. Adequate mixture pressure within each burner is maintained forcing the mixture outwardly through each outlet at a high velocity as compared to the prior art burners which allow the mixture to slowly flow through the outlets. The mixture flows through outlets 41, 42 and 43 at a velocity of 2,000 to 25,000 ft./min. In one embodiment of the invention, paperboard 52 was moved at 800 to 1,000 ft./min. with the mixture outlet velocity being 2,500 ft./min. increases in mixture outlet velocity allows for an approximate linear increase in the velocity of the paperboard. The air/gas ratio of the mixture is relatively high as compared to the air/gas ratio of the mixtures of the prior art burners. The lean mixture discharged by outlets 41, 42 annd 43 burns at a high temperature resulting in a high ionization level in the flame. Thus, paper board 52 may be moved past the high temperature, lean and highly ionized flame at a faster speed as compared to paperboard speeds possible with the prior art burners. Considerable fuel savings result due to the utilization of the lean mixture. A pair of flame retaining walls 44 and 45 are fixedly mounted to the main body of the sealer burner for compressing the flow of air and gas outwardly from the sealer burner thereby increasing the forward velocity of the flame and providing increased heat transfer to the paperboard 52 moving beneath the flame in a direction along the lengths of the burners. The rapid flame causes air to flow quickly on the outside in the direction of arrows and 71 thereby cooling walls 44 and 45. The main body of the sealer burner is mounted to and between a pair of vertical walls 46 mounted to posts 47 secured to bracket 48 of frame 11.

Air nozzle 17 will now be described, it being understood that a similar description applies to air nozzle 16. The main body of air nozzle 17 is mounted to and between a pair of vertical walls 49 secured to bracket 48. The main body of air nozzle 17 is provided with a hollow interior 50 connected by conduit 51 to a flexible hose 27 (FIG. 1) which in turn is connected by appropriate conduits to the air compressor to receive compressed air therefrom. Air nozzle 17 is provided with an aperture 64 which blows a curtain of air upward in the direction of arrow 65. Paperboard 52 moves along the lengths of sealer burners and air nozzles. In addition, the paperboard is disposed between each sealer burner and air nozzle. Flame 53 (FIG. 2) is in contact with retaining walls 44 and 45 and is directed outwardly to' ward one edge 54 of paperboard 52 at an acute angle 55 with respect to the paperboard. The air curtain from the air nozzle 17 extends upwardly at an angle of approximately 10 with respect to the vertical to carry the combustion by-products of flame 53 away from paperboard 52. Likewise, air nozzle 16 provides an upwardly directed air curtain to carry away the combustion byproducts of' the downwardly extending flame from sealer burner 12. As shown in FIG. 1, sealer burners 14 and 15 have flame retaining walls 56 and 57 which extend upwardly thereby directing the flame upwardly against the bottom surface of paperboard 52 as distinguished from the flames of sealer burners l2 and 13 which direct the flames downwardly against the top surface of the paperboard. The continuous flames from' sealer burners 14 and 15 extend upwardly allowing normal convection to carry the combustion by-products upwardly. The continuous flames from sealer burners 14 and 15 are directed at an acute angle with respect to the paperboard toward the edge of paperboard 52 opposite of edge 54. Paperboard 52 may be subsequently folded to position the top surface of edge 54 adjacent to the bottom surface of the opposite edge 54 to allow the melted coating to eventually solidify and to secure the opposite edges together forming a seam. Pressure rollers may be utilizedsubsequent to the heat sealing of the opposite edges to force the edges together.

The flame retaining walls on each sealer burner are provided with a plurality of gaps to allow for the expansion and contraction of the walls. For example, walls 44 and 45 of sealer burner 13 (FIG. 3) are provided with gaps 60. A flame detector 61 is mounted to bracket 62 secured to sealer burner 13. Likewise, the other sealer burners are provided with flame detectors to allow for the automatic detection of the flame. Each sealer burner is provided with an ignitor which may be similar to a spark plug. For example, sealer burner 13 is provided with ignitor 63 for the automatic ignition of the flame.

Any commercial fuel may be used with the present apparatus such as natural, coke oven, propane or butane. Also, blends of these particular gases may be utilized. The gas supply pressure should be bbetween 0.25 to l lb./sq.in. A source of gas pressure of at least 0.20 psi should be provided. For the four burner flame sealing system disclosed herein, the gas supply volume should be sufficient to produce 360,000 BTU/hr. or 360 cu.ft. of natural gas per hour. Generally, it is a good practice to oversize the gas supply pipes to assure a constant pressure. The burners should be spaced approximately 0.7 to 0.3 inches clearance from the paperboard. The burners may be rotated to adjust flame angle 55 to develop a desired width of heat application. In order to produce the greatest reliability and the best seal quality, it is important to have a very sharp blue flame which is lean. By adjusting air valves 36, the amount of air mixed with the gas will be controlled. Air valves 36 each consist of a threaded member having a disc mounted to the bottom end thereof which is positioned within housing 25. Each disc covers an aperture through which the air flows from housing 25 into the venturi housings. A lean mixture of gas and air will produce the clear blue flame. Excessive gas or a rich mixture will produce a yellow to blue-green flame color.

The internal cross-sectional area of each flame sealer is at least three times the total area of the gas outlets on each flame sealer. For example, the internal crosssectional area of the interior 40 (FIG. 2) of sealer burner 13 which extends perpendicular to the longitudinal axis of the flame sealer is at least three times the total cross-sectional area of all of the apertures 41, 42 and 43 which extend the length of the flame sealer as shown in FIG. 3. Thus, sufficient pressure exists within each flame sealer to force the mixture outwardly producing an intense, sharp flame when ignited. Suitable conveying means 70 (FIG. 4) are provided to support and convey the paperboard past the flames. The conveying means may include a plurality of rollers. Sealer burners 12 and 13 have aligned longitudinal axes whereas sealer burners l4 and 15 have aligned longitudinal axes.

The method of flame sealing the paperboard includes forcing a gas/air mixture from outlets extending along the length of an elongated tube under sufficient pressure to produce a continuous flame extending the length of the tube. The forcing step includes directing a gas/air mixture into the elongated tube and then restricting the total cross-sectional area of the outlet of the tube so that the internal cross-sectional area of the tube is at least three times greater than the total crosssectional area of the outlets. Sufficient air must be mixed with the gas which is then ignited in order to produce a blue and lean flame. The flame is then directed at an acute angle with respect to the paperboard with the tip of the flame being either impinged upon or spaced apart from the paperboard. All but the tip of the flame is enclosed in a trough on the tube which compresses the flame and increases the forward velocity of the gas/air mixture. In the embodiment shown in the drawings, the continuous flames from two of the flame sealers are directed at a downward angle with respect to the paperboard whereas pressurized air is forced upwardly to convey the combustion by-products away from the paperboard. The remaining two flame sealers 14 and 15 are positioned beneath the paperboard and direct a pair of continuous flames upwardly against the bottom surface of the paperboard. All of the flames are positioned at an acute angle with respect to the paperboard. In the embodiment shown in the drawings, the gas outlet holes of each flame sealer have uniform diameters to obtain a constant flame. By increasing the velocity of the gas/air mixture from the flame sealers with the retaining walls and the pressure within the flame sealers, the mixture is caused to be more turbulent thereby increasing the temperature to achieve higher heat transfer. The higher temperatures result since a high aeration rate is obtained. In addition, with a higher aeration rate, the burning rate increases and the flame geometry decreases with more complete combustion being obtained.

The apparatus and method disclosed herein is particularly useful in seaming together the opposite edges of a paperboard having a meltable coating thereon. In addition, the apparatus and method disclosed herein is particularly useful in flame priming paperboard for the subsequent attachment of aluminum foil onto the paperboard. Likewise, the invention disclosed herein may be utilized to dry any coatings such as ink coatings which have been placed on the paperboard. A primary advantage of the invention disclosed herein is to obtain a superior bond between paperboard which has been heated for the subsequent attachment of polyethylene. Best results have been obtained by making the internal cro s s sectional area of each sealer burner to be three times or greater than the total cross-sectional area of the gas outlets on a particular sealer burner.

Parts of Gas/Parts of Air Natural gas l/lO Coke oven gas l/5 /z Propane 1/25 Butane 1/32 l lajm; 4 V r 7 7 W H premixing sufficient air with said gas prior to said i 1. An apparatus for flame treating paperboard cOmforcing step to insure complete combustion of the prising: gas; and,

a frame; igniting said mixture to produce a flame with length;

a Source Of Pressurized air; 5 directing said flame toward and adjacent a papera Source f Pr su i g board to directly heat said paperboard with said valve means connected to said source of air and said fl m whil id paperboard moves along id source of gas and mounted on said frame operable l h f id fl to Provide a lean mixture of g to 7. The method of claim 6 andcomprising the addia first elongated tube with a longitudinal axis, said 10 tiona] Steps f;

tube Peing mounted on said frame and connected enclosing all but said tip of said flame in a trough on to said source of air and said source of gas, said said elongated tube; tube having an interior cross-sectional area extenddirecting i flame at a downward angle with respect ing perpendicular to said axis, said tube having a to Said paperboard; plurality of Outlets extending along Said longitudi' forcing pressurized air upwardly from an air nozzle nal axis to form an elongated strip of gas and air espositioned beneath Said paperboard to convey caping through said outlets, said cross-sectional combustion byproducts fr id fl m away area of said tube being at least three times the total f id paperboani cross-Sectional area of said Outlets; n "i'Aihniodbr' flameimating paperboard while pre- 3 P of pp flame directing walls on Said tube venting scorching thereof comprising the steps of:

with Said Outlets extending therebetween and providing an elongated tube with length and outlets tending along said axis with at least a portion of along id l th; said flame extending between said walls being comforcing a gas/air mixture from said outlets under sufpressed therebetween, said walls are spaced apart ficient pressure to produce a first intense, continuforming a trough in which said gas burns; and, ous flame extending said length when ignited;

conveying means mounted on said frame and suppre-mixing sufficient air with said gas prior to said porting said paperboard operable to convey said forcing step to insure complete combustion. of the paperboard past said trough and said flame therein. g

2. The apparatus of claim 1 and further comprising: igniting said mixture to produce a flame with length;

a second elongated tube mounted to said frame bedirecting Said flame toward and adjacent a P p neath said conveying means and extending parallel board to directly heat Said Paperboard with i to said axis of said first tube, said second tube being flame while: Said Paperboard moves along Sald connected to said source of pressurized air and lengih of Said flame} having an air outlet opening upwardly enclosing all but the tip of said flame in a trough on 3. The apparatus of claim 2 wherein: sald elong,ated tube;

said first elongated tube is positioned with respect to dlrectmg Said flame at a downward angle with respect said sheet to direct said flame outwardly against an 9 paperimrdi edge of said sheet forming an acute angle between q pressunzed uPwardly from an nozzle Said Sheet and Said flame positioned beneath said paperboard to convey 4. The apparatus of claim 2 wherein: fcombustion by-products from said flame away rom said paperboard,

said paperboard has a meltable coating thereon and one art of gas is mixed with at least five arts air a first edge portion positioned beneath said flame g to i men p and a second edge portion and further comprising: g as 6f 'daim 7 wherein,

a thud elongated .tube mounted to Sal.d frame and said paperboard has a first edge portion positionable connected to said source of pressurized gas and beneath said flame and a Second edge portion and said valve means, said third elongated tube is subfurther comprising the additional Steps of: stantially identical to said first elongated tube exdirecting a second continuous flame Substantially cept said third elongated tube has gas outlets openidentical to Said first continuous flame upwardly ing upwardly with a flame extending therefrom in an upward direction against said second edge portion. I

5. The apparatus of claim 4 wherein:

against and at an acute angle with respect to said .991 jd sle t wi.

10. A method of flame treating paperboard with a highly ionized and high temperature flame while preventing scorching of the paperboard comprising the steps of:

Lil

said source of pressurized air includes an air blower 5 connected to said second elongated tube;

said source of pressurized gas includes at least one valve to control flow of gas to said first and third elongated tubes;

along said length;

forcing a gas/air mixture from said outlets under sufficient pressure to produce a first intense, continuousflame extending said length when ignited;

mixing gas and air to produce a lean mixture of gas to air; accumulating said mixture in a tube having a certain Said conveying means is Operable to more Said P p 60 cross-sectional area extending perpendicularly to board into Contact with Said flamethe longitudinal axis of said tube, said tube having A method of flame treating p p i while P outlet ports with said mixture being at a certain venting scorching thereof comprising the steps of: pressure;

providing an elongated tube with length nd ut allowing said mixture to escape through said outlets to produce an elongated strip of ignitable mixture extending along said tube;

forcing said mixture through each port at a high velocity to promote mixing of ambient air with said mixture and complete combustion of said mixture when ignited;

igniting said mixture to produce an elongated flame extending along said tube subsequent to said forcing step; and,

directing said flame toward and adjacent said paperboard to directly heat said paperboard with said flame;

moving said paperboard along said elongated flame.

11. The method of claim 10 wherein:

said directing step includes the step of directing the tip of said flame to impinge upon said paperboard.

12. The method of claim 10 and further comprising:

compressing in a trough portions of said flame adjacent said tube to increase forward velocity of said flame while allowing portions of said flame to extend outwardly of said trough sucking into said flame ambient air.

13. The method of claim 10 and further comprising:

directing said flame downwardly with respect to said paperboard; and,

conveying combustion by-products from said flame away from said paperboard during the time said flame is adjacent said paperboard, said conveying step includes the step of forcing pressurized air upwardly from an air nozzle positioned beneath said paperboard.

14. The method of claim 13 wherein:

said step of directing said flame downwardly includes the step of directing said flame at an acute angle with respect to said paperboard.

15. The method of claim 10 wherein:

said directing step includes the step of directing said flame toward an edge of said paperboard and the step of directing the tip of said flame to contact only a single side of said edge without wrapping around said edge and contacting a side of said paperboard opposite said single side.

UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 3,870,461 Dated March 11, 1975 In Walter G. Wise It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 2 change "flame" to "frame" Column 7, line 60 change "more" to "move" Signed and sealed this 27th day of May 1975.

(SEAL) Attest C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks USCOMM'DC 6Q376-P69 UJ. GOVIINMINI PIINYING OIIIC! "0' 0-06!!! ORM PO-IOSO (10-69) 

1. An apparatus for flame treating paperboard comprising: a frame; a source of pressurized air; a source of pressurized gas; valve means connected to said source of air and said source of gas and mounted on said frame operable to provide a lean mixture of gas to air; a first elongated tube with a longitudinal axis, said tube being mounted on said frame and connected to said source of air and said source of gas, said tube having an interior cross-sectional area extending perpendicular to said axis, said tube having a plurality of outlets extending along said longitudinal axis to form an elongated strip of gas and air escaping through said outlets, said cross-sectional area of said tube being at least three times the total cross-sectional area of said outlets; a pair of opposite flame directing walls on said tube with said outlets extending therebetween and extending along said axis with at least a portion of said flame extending between said walls being compressed therebetween, said walls are spaced apart forming a trough in which said gas burns; and, conveying means mounted on said frame and supporting said paperboard operable to convey said paperboard past said trough and said flame therein.
 2. The apparatus of claim 1 and further comprising: a second elongated tube mounted to said frame beneath said conveying means and extending parallel to said axis of said first tube, said second tube being connected to said source of pressurized air and having an air outlet opening upwardly.
 3. The apparatus of claim 2 wherein: said first elongated tube is positioned with respect to said sheet to direct said flame outwardly against an edge of said sheet forming an acute angle between said sheet and said flame.
 4. The apparatus of claim 2 wherein: said paperboard has a meltable coating thereon and a first edge portion positioned beneath said flame and a second edge portion and further comprising: a third elongated tube mounted to said frame and connected to said source of pressurized gas and said valve means, said third elongated tube is substantially identical to said first elongated tube except said third elongated tube has gas outlets opening upwardly with a flame extending therefrom in an upward direction against said second Edge portion.
 5. The apparatus of claim 4 wherein: said source of pressurized air includes an air blower connected to said second elongated tube; said source of pressurized gas includes at least one valve to control flow of gas to said first and third elongated tubes; said conveying means is operable to move said paperboard into contact with said flame.
 6. A method of flame treating paperboard while preventing scorching thereof comprising the steps of: providing an elongated tube with length and outlets along said length; forcing a gas/air mixture from said outlets under sufficient pressure to produce a first intense, continuous flame extending said length when ignited; pre-mixing sufficient air with said gas prior to said forcing step to insure complete combustion of the gas; and, igniting said mixture to produce a flame with length; directing said flame toward and adjacent a paperboard to directly heat said paperboard with said flame while said paperboard moves along said length of said flame.
 6. A method of flame treating paperboard while preventing scorching thereof comprising the steps of: providing an elongated tube with length and outlets along said length; forcing a gas/air mixture from said outlets under sufficient pressure to produce a first intense, continuous flame extending said length when ignited; pre-mixing sufficient air with said gas prior to said forcing step to insure complete combustion of the gas; and, igniting said mixture to produce a flame with length; directing said flame toward and adjacent a paperboard to directly heat said paperboard with said flame while said paperboard moves along said length of said flame.
 7. The method of claim 6 and comprising the additional steps of: enclosing all but said tip of said flame in a trough on said elongated tube; directing said flame at a downward angle with respect to said paperboard; forcing pressurized air upwardly from an air nozzle positioned beneath said paperboard to convey combustion by-products from said flame away from said paperboard.
 8. A method of flame treating paperboard while preventing scorching thereof comprising the steps of: providing an elongated tube with length and outlets along said length; forcing a gas/air mixture from said outlets under sufficient pressure to produce a first intense, continuous flame extending said length when ignited; pre-mixing sufficient air with said gas prior to said forcing step to insure complete combustion of the gas; and, igniting said mixture to produce a flame with length; directing said flame toward and adjacent a paperboard to directly heat said paperboard with said flame while said paperboard moves along said length of said flame; enclosing all but the tip of said flame in a trough on said elongated tube; directing said flame at a downward angle with respect to said paperboard; forcing pressurized air upwardly from an air nozzle positioned beneath said paperboard to convey combustion by-products from said flame away from said paperboard; one part of gas is mixed with at least five parts air prior to ignition.
 9. The method of claim 7 wherein: said paperboard has a first edge portion positionable beneath said flame and a second edge portion and further comprising the additional steps of: directing a second continuous flame substantially identical to said first continuous flame upwardly against and at an acute angle with respect to said second edge portion.
 10. A method of flame treating paperboard with a highly ionized and high temperature flame while preventing scorching of the paperboard comprising the steps of: mixing gas and air to produce a lean mixture of gas to air; accumulating said mixture in a tube having a certain cross-sectional area extending perpendicularly to the longitudinal axis of said tube, said tube having outlet ports with said mixture being at a certain pressure; allowing said mixture to escape through said outlets to produce an elongated strip of ignitable mixture extending along said tube; forcing said mixture through each port at a high velocity to promote mixing of ambient air with said mixture and complete combustion of said mixture when ignited; igniting said mixture to produce an elongated flame extending along said tube subsequent to said forcing step; and, directing said flame toward and adjacent said paperboard to directly heat said paperboard with said flame; moving said paperboard along said elongated flame.
 11. The method of claim 10 wherein: said directing step includes the step of direcTing the tip of said flame to impinge upon said paperboard.
 12. The method of claim 10 and further comprising: compressing in a trough portions of said flame adjacent said tube to increase forward velocity of said flame while allowing portions of said flame to extend outwardly of said trough sucking into said flame ambient air.
 13. The method of claim 10 and further comprising: directing said flame downwardly with respect to said paperboard; and, conveying combustion by-products from said flame away from said paperboard during the time said flame is adjacent said paperboard, said conveying step includes the step of forcing pressurized air upwardly from an air nozzle positioned beneath said paperboard.
 14. The method of claim 13 wherein: said step of directing said flame downwardly includes the step of directing said flame at an acute angle with respect to said paperboard. 